Lubricating composition



Patented Dec. 18, 1951 2,579,037 LUBRICATING COMPOSITION Elliott Alfred Evans and John Scotchford Elliott, London, England, assignors to C. C. Wakefield & Company British company Limited, London,

England, a

No Drawing. Application December 6, 1948, Se-

rial No. 63,843. In Great Britain December 9,

1; The present invention comprises improvements in or relating to lubricating compositions and relates more particularly, though not exclusively, to lubricating compositions for use in internal combustion engines which may be either petrolor oil-operated. In the latter case the invention is applied to the so-called heavy duty lubricating oils employed in diesel or other types of oil engines.

. It is an object of the invention to provide a lubricating composition in which the tendencies of the lubricant to form products corrosive to metals (e. g. metal bearing surfaces) and to form deleterious oxidation products in the lubricant are inhibited. It is a further object of a preferred form of the invention to provide a lubricating composition possessing also detergent properties which tend to secure a clean running engine during use of the composition by preventing the deposition of gum or lacquer in the lubricated parts and maintaining solid particles and sludge (formed in any part of the engine or in the lubricant) in suspension in the lubricant. Such properties are of particular importance in the operation of oil engines such as diesel engines.

The present invention contemplates the use in a lubricating composition of a metallic derivative of an organic substituted dithiophosphate.

It has already been proposed to add a variety of metal salts of organic dithiophosphoric acids to oils.

These additives are known in general to impart to the oil good resistance to oxidation and to inhibit to a greater or less extent the formation of products corrosive to composite metal bearings.

Some of them also possess detergent or sludge dispersive properties, especially effective in this connection being the alkaline earth metal salts of the straight chain dithiophosphoric acids having ten or more carbon atoms.

It has been found, however, that these dithiophosphates of relatively high molecular weight are much less effective as inhibitors of oxidation and bearing corrosion than those of low molecular weight, which latter, however, are relatively ineffective as detergents and sludge dispersing agents.

It has been found, surprisingly, that the par- 7 15 Claims. (01. 25.2-48.6)

In this respect the salts of metals of groups 2 and 3 of the periodic table are especially effective, but the salts of other metals are also very satisfactory additives from the point of view of this invention especially as regards the inhibition of oxidation and corrosion of composite metal bearings.

The additives of the present invention also confer upon the base oil an improved film rupture strength. According to the present invention a, lubricating composition comprises a lubricating oil base and a minor proportion of a metal salt (which is soluble in the oil base) of an organic (ii-substituted dithiophosphoric acid derived at least in part from a saturated aliphatic hydroxyether. Such a di-substituted salt can be represented by the general formula where n represents the valency of a metal M, R1 is a saturated aliphatic radicle containing an ether grouping, and R2 is any suitable organic radicle.

One type of metal salt of the above character incorporated in a lubricating oil base in accordance with the present invention is one derived from tetrahydrofurfuryl alcohol, i. e., a salt in which radicle R1 of the above formula is a tetrahydrofurfuryl radicle represented by the formula CH2--CH1 -H: CH2

The radicle R2 is then some other suitable organic radicle since the dietetrahydrofurfuryl dithiophosphates are found to be insoluble in a lubricating oil base.

Examples of other aliphatic hydroxy-ethers from which the metal salt may be derived, however, are: Ethylene glycol monobutyl ether (C4H9OCH2CII2OH), diethylene glycol monoethyl ether (C2H5OCH2CH2OCH2CH2OH), 3- methoxy-n-butanol, and triethylene glycol monobutyl ether. Examples of organic hydroxylic compounds from which the radicle R2 of the above formula may be suitably derived are:

Appropriate radicles for R1 and R2 in the general formula quoted above will always be such that the (ii-substituted metal salt is soluble in the lubricating oil base. The radicle Ra should possess at least 5 carbon atoms.

Specific examples of disubstituted dithiophosphoric acids a metal salt of which is employed in accordance with the invention are: Tetrahydrofurfuryl octyl-cresyl dithiophosphoric acid and di-(p-butoxyethyl) dithiophosphoric acid.

3-methoXy-n-butyl Z-ethyl hexyl dithiophosphoric acid. 1

Ethylene glycol monoethyl ether lauryl dithiophosphoric acid. a

The soluble metal salts may be employed of any of the following metals: barium, calcium, strontium, magnesium, zinc,-a luminium, nickel, cobalt, tin, cadmium, chromium, manganese and thallium.

Conveniently a proportion of from 0.2% to 2.0% by weight of the metal salt is employed in the lubricating composition; and in one form of the invention the lubricating composition in- *i :cludes' also a small proportion of an oil-soluble metal salt'of a petroleum sulphonic acid. The latter component may conveniently be added in a proportion of from 0.05% to 2.0% by weight of the composition. More particularly in the case where a chromium dithiophosphate is employed the conjoint use of tin petroleum sulphonate is preferred.

Some of the metal salts contemplated in this invention have only a limited degree of solubility in mineral oil. True solutions of such compounds may, however, be obtained by dissolving them first in concentrated oil solutions of the metal petroleum sulphonates and then eifecting solution in the mineral oil in the desired proportion. 7

Examples of compounds with a limited oil-solubility which may be solubilised in this way are Zinc salt of di(2-butoxy2ethoxyethyl)dithiophosphoric acid Calcium salt of di(p-butoxyethyl) Cobalt salt of 2methoxy -2-ethoxyethyl methyl cyclohexyl dithiophosphoric acid It is, however, preferred to employ salts which weight in the region of 400-500. Any polyvalent metal petroleum sulphonate, or mixtures thereof may be employed, special preference being given to the tin salts. Other metal salts may however be used with beneficial results e. g. those of calcium, barium, strontium, magnesium, aluminium, chromium, manganese, cadmium, nickel, cobalt, zinc and thallium.

The conjoint use of metal petroleum sulphonates and the metal dithiophosphates of this invention provides lubricants possessing excellent detergent properties, such lubricants being especially suitable as heavy duty lubricants for use in high-speed diesel engines where high loads and piston temperatures are encountered.

4 V Preparation of the metal salt of the di-substituted dithiophosphoric acid is conveniently effected by first reacting the aliphatic hydroxyether with phosphorus pentasulphide, and Where a mixed organic dithiophosphate is desired an appropriate hydroxylic organic compound may be admixed with the hydroxyether for simultaneous reaction with the phosphorus pentasulphide. The acid may be neutralised by caustic soda and. a desired metal salt produced by the addition of a suitable salt of the said metal.

The following examples are given in some detail.

Example I.-P1-eparation of chromium tetfahydrofurfur'yl octyl-cresyl dithiophospihate 772 gms. of tetrahydrofurfuryl alcohol were mixed with .1650 gms. of octyl cresol'ina 5-litre flask, heated to 130? C., and treated with 915 gms. of powdered phosphorus pentasulphide added in small quantities with stirring, The

7 temperature was maintained at 130-140? C. for

iii)

about 30 minutes until the reaction was almost complete and most of the phosphorus ,pentasub phide had disappeared. The reaction was then completed by heating slowly to 150 C. and maintaining this temperature with stirring forffive minutes. I a

After cooling, the product was dissolved in petroleum ether and .filtered from a little sulphur and unreacted phosphorus pentasulphide,

the solvent being then distilled off under reduced pressure, yielding an amber viscous liquid. It

will be appreciated that in addition to the mixed thiophosphate there is present. in .this liquid lesser amounts of di(tetrahydrofurfury1) dithiophosphate and of di(octylcresyl) dithiophosphate. The acidity of the product, determined by titrating an alcoholic solution with standard caustic soda solution in the presence of a phenolphthalein indicator, corresponded to anapparent molecular weight of 457 (theoretical 417) and indicated that the reaction was 91% complete.

94 grams of this reaction product were now mixed with 840 cos. of Water in a 3-litre beaker, heated to 40 to 50 -C., and made just alkaline to phenolphthalein by adding 10% caustic soda solution with stirring. This aqueous solution of the sodium thiophosphate was then. heated to C.

and a further small amount of caustic soda added, a clear solution just alkaline to phenolphthalein thereby being obtained.

To this solution was added slowly with stirring 370 cos. of nearly boiling 10% aqueous chrome alum, when the purple chromium salt of the dithiophosphatewas precipitated as a viscous liquid. Q

After cooling, the aqueous solution was decanted from the almost solid substance which was then dissolved in 500 cos. of petroleum ether, dried by refluxing under a constant water separator, filtered from a quantity of insoluble green solid, and freed from solvent by distillation.

The yield Was 77% of the theoretical. V The product contained 2.02% of chromium, the calculated chromium content being 3.79%, representin a 53% conversion to the chromium salt,

the principal impurities being the freedithiophosphoric acid, its sodium salt, and a certain amount of free octyl cresol produced by hydrolysis. V

It was subsequently found that by carrying out the precipitation at 50-60 C. a better conversion to the chromium salt could be obtained.

It will be understood that in employing the compounds of this invention either pure metal salts may be used or mixtures such as-the product of Example I. While minor amounts of the free dithiophosphoric acids and their sodium salts in the products are not objectionable, it is preferred to utilise materials containing not more than about of the free acid (and preferably less) and not less than about 65% of the polyvalent metal salt.

If desired, the residual free acid may be substantially neutralised by heating the product (preferably in oil solution) with a metal oxide or hydroxide (such as zinc oxide or calcium or barium hydroxide) to produce, for example, a mixture of chromium and zinc salts associated with a minor amount of sodium salt.

The product of Example I is represented by the formula Example II.Preparation of zinc di butoxyethyl) dithiophosphate tered, and the solvent removed by distillation.

The acidity of the product corresponded toa molecular weight of 370 (calculated 330) i. e. conversion to the dithiophosphate was 88% complete.

18.5 grams of this substance were mixed with 100 cos. of water and made just alkaline to phenolphthalein at room temperature. The solution was then heated to 90 C. decanted from a little brown oily liquid which separated and treated at 90 C. with a slight excess of hot aqueous zinc chloride solution. A white opaque liquid was precipitated.

After cooling, the aqueous solution was decanted, and the product dissolved in petroleum ether, dried by refluxing under a constant water separator, and filtered, the solvent being finally removed by distillation.

The zinc salt was clear pale yellow liquid readily soluble in oil.

The product of Example 11 is represented by the formula clmocmcmo s P\ Zn olmoomomo s Example III A lubricating composition was produced by in corporating in a mineral lubricating oil base 0.8% by weight of the product of Example I and 0.2% of tin petroleum sulphonate.

6 Example IV.Preparation of cadmium "dim-butozryethyl) dithiophosphate 33.5 grams of di(,c-butoxyethyl) dithiophosphate prepared as described in Example II were mixed with 636.5 cos. of water and caustic soda added gradually with stirring at room temperature until neutralisation was complete. The solution was filtered from a little insoluble material, heated to 50 C. and treated with a warm 10 per cent solution containing 12.5 grams of cadmium chloride, when the cadmium. salt was precipitated as a yellowish-white crystalline solid.

After recrystallisation from petroleum ether it was obtained in the form of fine white needles in 36 per cent yield. It contained 15.2% of cadmium as compared with a theoretical cadmium content for the pure salt of 14.6%.

Example V.-Preparation of zinc salt of 3-methioaty-n-butyl Z-ethyl hexyl dithiophosphoric acid By the method of Example II there were obtained from the reaction between a mixture of 32.5 grams of 2-ethyl hexanol and 26 grams of 3-methoxy-n-butanol with 27.8 grams of phosphorus pentasulphide during 15 minutes at -110 C. and finally 5 minutes at C., 75 grams of 2-ethyl hexyl 3-methoxy-n-buty1 dithiophosphoric acid, representing a 91% yield. The molecular weight was 375, as compared with a theoretical value of 328.

37.5 grams of this material were mixed with 4.4 grams of zinc oxide and heated slowly with stirring to C. during about 20 minutes, after which the product was cooled, dissolved in petroleumether, filtered from excess zinc oxide, and freed from solvent by distillation. 5

By thismeans there were obtained 36.6 grams (91 per cent yield) of a viscous yellow liquid containing 6.46% of zinc, as compared with a theoretical content of 7.70%. V

The method of Example V is generally ap' plicable for the preparation of the zinc and magnesium salts contemplated by this invention, the method of Example IV being more widely applicable to the salts of any of the polyvalent metals. Other known methods may, however, be adopted, e. g. direct reaction between the'free acid and a metal oxide in alcohol-benzene solution at 40-50" C. (applicable especially to the alkaline earth metal and magnesium salts) or direct reaction between a metal hydroxide, such as barium hydroxide, and free acid by heating together in mineral oil solution in presence of a current of air to remove liberated water. Alternatively metathesis may be carried out in alcoholic solution between an alkali metal salt of a dithiophosphoric acid and an alcohol-soluble metal salt.

The product of Example V is represented by the formula onlomomcmonomo S TEST RESULTS Test 1.O:m'dation resistance I As a means of examining the oxidation resistance of the compositions proposed by the present invention, a modification of the well-known British Air Ministry oxidation test was employed. Lubricating compositions were oxidised under the standard conditions of the British Air Ministry oxidation test except that a temperature of 160 C. was employedand that a copper catalyst, consisting of a rolled polished piece of copper foil 2 x 1", waspresent. The catalyst was replaced by a fresh one at the end of the first period of 6 hours oxidation.

The test results obtained were:

8 heated in a circular electrically heated oil bath thermostatically controlled to maintain the lubricant temperature at 140 C. c The beakers were equipped with closely fitting aluminium covers having central slides which were normally closed but capable of being opened for the insertion of a test specimen. The slides when closed allowed sufiicient clearance for centrally placed steel stirring rods to revolve freely. The latter were electrically driven from a common driving shaft at 400: R. P. M. and carried at their lower end slotted holders to which lead test-pieces wereattached by means of screws. For the test-pieces rectangular plates of pure lead 1% by 1" were mounted vertically just below the surface of the lubricant with the longer axis horizontal. Copper strips, as catalysts, /2" wide and bent into a semicircle 3%," in diameter were placed wholly below the surface of the lubricant and attached by means of vertical'copper wires to corks fitted in the beaker covers. Each beaker was also fitted with a thermometer.

Tests were conducted for a maximum total time IPerlcetnlt use 11 e Test Viscosity gig??? in pet Lubricating Composition Increase ether, (per cent) Kolnmper (B. P

' mm below 40 O 1 Oil A (average figures) 33. 6 0O 0. 2 Oil "A"+l% Manganese 3-methoxy-n-butyl Z-ethyl hexyl 23. 8 0.56

dlthiophosphate. 3..." Oil A+0.5% Cobalt 2-methoxy-2-ethoxyethyl methyl cyclohexyl dithiophosphate 23. 5 0. 45 D0. +10% Cadmium petroleum sulphonate.

1 Very slight trace.

Additives marked with an asterisk were not soluble in mineral oil in the proportions employed in the absence of the metal petroleum sulphonate.

Oil A as employed in these and in ensuing tests consisted of a blend of 94% of a solvent refined parafiinic type mineral oil of viscosity about 150 seconds Redwood at 140 F. and 6% of a blend of viscosity about 330 seconds Redwood at 140 F. containing a brightstock.

Test 2.-Bearing corrosion The following test was employed for obtaining information as to the tendency for corrosion of composite metal bearings, particularly copperlead bearings, to occur in use of lubricating compositions provided by the invention.

' 400 ml. of lubricant was weighed into 1500 ml.

of 30 hours in periods of six hours, the copper and lead specimens being removed every two hours and replaced by fresh clean ones. Copper catalysts were cleaned with carborundum powder and washed in petroleum ether. Lead specimens were flattened, scraped with a special Skartsen scraper and finally polished, by brushing in one direction with a type of stiff wire brush known as file carding" before washing in benzene and weighing. After a 2-hour period a further washing in benzene, brushing with a camel hair brush and re- Weighing was effected; The cumulative corrosion at any given time was calculated'by adding together the Weight losses of the lead specimens after each 2 hour period. These cumulative losses were plotted against time, and from the curves obtained, the times required for certain fixed corrosion losses to be reached, were read off.

tall lipless glass beakers, eight of which were The following results were obtained:

Lead specimen weight Hours run to weigh T t loss (rugs) loss of- 1 7 Lubricating Composition 7 after 12 18 20 50 100 hrs. hrs. mgs. mgs. mgs.

4 Oil A (average flguresyuni 238 4 6 8 5 O l A+0.5% T n diQB-butoxyethyl) dithiophosphate 28 44 6 20 29 6 O l A+0.5% Nickelfiethoxyethyl lauryl dithiophosphate 4 27 9 over 30 7 011 A+0.4% Zinc (11 (3-methoxy-n-butyl) dithiophosphatc 1 14 15 17 20 8 s22; as

- 1 a mium i u oxyet y ithiop osp a +2.09% Barium petroleum sulphonate 12 18 20 over 30 9 O1l.A.+0.6% Magnesium di(2-butoxy-Z-ethoxyethyl) dithiophosphate 35 97 8 l3 l8 +10% Nickel petroleum su1phonate 10 011 A"+0.4% Chromium tetrahydroiurfuryloctyl cresyl dithiophosphate 1 17 58 13' 17 20 +01% Tm petroleum Sulphonate n,

1 This compound contained about 72% of actual chromium salt.

Test 3.-Gum, lacquer and carbon formation A simple test was devised to compare the tendencies of oils to deposit gum, lacquer and carbon on hot metal surfaces such as piston walls and heads in internal combustion engines.

Rectangular aluminium blocks (12" x 2" x A) were cleaned by rubbing with pumice and water and finally by washing with petroleum ether. They were then clamped in a special holder at an angle of 25 to the horizontal and heated at the upper end by means of a Bunsen burner.

A steady temperature gradient down the block was thus soon obtained, the block being shielded from the name by means of an asbestos sheet.

The oil under test was now dropped from a burette on to the block at a point, the temperature of which was 350 C., (as measured by a pyrometer). at a rate of approximately 1 cc. per minute for a total of 30 minutes, after which the block was allowed to cool and washed free from L oil with petroleum ether.

til

Maximum extent of carbon or lacquer of various colours vertically below the top of the oil drop-point.

This central portion was often composed of several different types of lacquer superimposed on each other. The figures quoted were obtained by measuring from the top of the oil drop-point to the lowest point at which lacquer of a particular type could be discerned.

Four types of lacquer were discernible:

A heavy black deposit of carbon. A dark. brown deposit of lacquer. A light brown deposit of lacquer.

A pale yellow deposit of lacquer.

(1) and (2) correspond to a rating of on the Lausonpiston rating chart, (3) to a rating of about 4, and (4) to a rating of about 1.

The following results. were obtained: Oil B was a solvent refined parafiinic type mineral oil of viscosity about 150 seconds Redwood at 140 F.

Peripheral ridge Central deposit, Extent of of gum lacquer vertically (mms.) g Lubricating Composition M A a $1 3? tha Black 3 flight Yellow (mms.) (mms) wn own 11 Oil B (average figures) 5. 7 2-9 31 50 60" 12 Oil .B+0.5% Zinc dim-methyl isoamyl) dithiophosphate 6. 8 5.3 34. 5 49. 5 60 13 Oil B+0.5% Zinc di(2-ethyl hexyl) dithiophosphate 8. 0 4. 3 12 27 36 46 14 Oil B+0.5% Zinc diQS-butoxyethyl) d1- thiophosphate 5. 5 3. 5 l. 5 l. 5 8. 5 36 15 Oil B+0.5% Zinc 3-methoxy-n-butyl 2-ethyl hexyl dithiophosphate 2. 6 1. 4 Nil 4. 0 15 27 16 Oil B+O.5% Aluminium {i-ethoxy-ethyl lauryl dithiophosphate 6. 8 3.0 0 17 Oil B+0.5% Nickel B-ethoxy-ethyl lauryl dithiophosphaie. 4. 2 1. 5 Nil 1. 0 12 18 Oil B+0.5% Nickel methyl cyclohexyl) dithiophosphate 5. 5 3. 0 80 107 19 Oil B+0.5% Barium B-butoxy-ethyl nonyl dithiophosphate 4. 3 2. 6 15 17 20 Oil B+0.5% Barium di(decyl-dodecyl dithiophosphate 9.0 4. 7 33. 5 41 51 69 21 As test 14+0.5% tin petroleum sulphonatemu 6.0 3. 3 N il, 4. 5 20 41 22 As test 14+O.5% calcium petroleum snlphonate. 5.6 3.5 1.0 1.0 1.0 18 23 Oil B+0.5% Zinc di(2-butoxy-2-ethoxyethyl) dithiophosphate 2 +0.55%, Chromium petroleum sulpho- 4. 2 3.0 21 27 27 31 na e i This compoimd was the same as that employed in test 10. i This compound was prepared from a mixture of alcohols having 10-12 carbon atoms.

Deposits were in this way obtained on the blocks consisting of a peripheral ridge of gum, shaped like an inverted V and a central patch of lacquer or carbon varying in colour and extent according to the oil tested. The repeatability of the test was ood.

It was found that the addition of small quantities of many of the additives of this invention to a particular mineral oil effected a very marked reduction in the amount of gum, lacquer and carbon deposited, especially as regards the central portion of the deposit.

In order to express the results numerically, the following measurements of the deposits were made:

(01.) Maximum width of peripheral gum ridge.

(1)) Average width of peripheral gum ridge (mean of 8-10 measurements) for comparative purposes in tests 12, 13, 18 and .20. Tests 21 and 22 show that some additional improvements may be expected from the conjoint use of a metal petroleum sulphonate.

Test 4.--Lauson engine tests Tests were carried out in standard H-2 type Lauson engines, under the following conditions:

Jacket temperature 2J10i2 F. Oil sump temperature 280i2 F. Test duration hours Test results were as follows:

Used Oil Analysis Piston lacquer Bearing Per Cent Test Lubricant rating weight lnsol. Acidity No. (C. R.C. loss Per Cent in pet. (m S 7 visual (mgs.) viscosity eltgher, rating) lncrease V 11.01%. per gm) 24 gil i (average over tgstsynng 1 .2 E 1 i1 1 d t h 1 1 6. 2 92 39. 9 0. 94 1.04 i1 0.5 inc 3-met ox -nu e y exy 1 mp osphateniin? m 6.5 4 14.3 0.25 0. 39 26 Oil A" 0.8% Chromium tetrahydrofurfuryl octyl cresyl dithiophosphate 0.2% Tin petroleum sulphonate 6. 5 12. 5 43.6 0.48 0.50

It was observed in test 25 that the deposit on the piston head was of a soft oily nature which could be largely removing by wiping, whereas in all the tests carried out on oil A, this deposit was of a hard nature. Hard deposits were similarly obtained when the'simple metal dithiophosphates, already known to the art, were employed.

The C. R. C. visual rating was according to the method laid down by the Co-ordinating Research 7 Council for rating piston cleanliness in the standard Chevrolet 36-hour L-4 test, in which a clean piston would have a rating of 10.0.

Test 5.36-.hour Chevrolet test Tests were carried out on a ,G-cylinder Chevrolet engine of standard type and according to the Standard Co-ordinating Research Council procedure L-4.

The following results were obtained:

rated alicyclic radicals and saturated heterocyclic radicals containing only carbon and oxygen in the nucleus.

2. A lubricating composition comprising as a major ingredient a mineral oil base, said base having incorporated therein as an additive a small amount, sufficient to inhibit bearing cor-;,

rosion and oxidation of said oil and to substantially reduce the deposition of gum, lacquer and carbon, of an oil-soluble salt of an organic di- Uscd Oil Analysis Average Per Acidity Test 4 corrosion Piston Total Total Cent (mgs. No 011 Consumption loss per varnish varnish sludge Per insol. KOH

- whole rating rating rating Cent in pet per brg. (gms.) visc. ether gm.)

inc. (B. P

below C.)

27 Oil A" -n 0. 856 8. 4 48. 4 46. 0 52. 3 0.85 0.62 28 Oil A 0.8% Chromium tetrahydroiurturyl octyl cresyl dithiophosphate 0.2% tin petroleum sulphonate 0. 158 8. 9 48. 9 47. 0 43. 8 0. 54 0. 34

1 This compound was the same as that employed in test 10.

'having incorporated therein as an additive a small amount sufiicient to inhibit bearing corrosion and oxidation of said oil and to substantially reduce the deposition of gum, lacquer and carbon, of an oil-soluble salt of an organic dithiophosphoric acid represented by the general formula thiophos'phoric acid represented by the general formula wherein n represents the valency of the metal M,

R1 is a saturated radical free from aromatic substituents and containing an ether grouping and is selected from the group consisting of aliphatic radicals and heterocyclic radicals containing only carbon and oxygen in the nucleus and R2 is an organic radical having at least 5 carbon atoms and is selected from the group consisting of saturated aliphatic radicals, saturated aliphatic radi-p cals having an ether grouping, saturated alicyclic radicals, saturated heterocyclic radicals having only carbon and oxygen in the nucleus and alkylated benzene radicals in which the alkyl substituent is saturated.

3. A lubricating composition in accordance with claim 1 in which R1 and R2 are saturated aliphatic radicals free from aromatic substituents and containing ether groupings. V

4. A lubricating composition in accordance 13 with claim 1 in which the amount of said metal salt is between 0.2 and 2.0% by weight of the mineral oil base.

5. A lubricating composition in accordance with claim 4 in which R1 is a saturated aliphatic radical.

6. A lubricating composition in accordance with claim 5 in which R2 is a saturated aliphatic radical.

7. A lubricating composition in accordance with claim 1 in which the composition also contains a small amount, suificient to increase the detergent properties of the composition, of an oilsoluble metal salt of petroleum mahogany sulphonic acid.

8. A lubricating composition in accordance with claim 7 in which the amount of said salt of petroleum sulphonic acid is between 0.05 and 2.0 by weight of the mineral oil base.

9. A lubricating composition in accordance with claim 7 in which the salt of petroleum sulphonic acid is an alkaline earth metal petroleum mahogany sulphonate.

10. A lubricating composition in accordance with claim 7 in which the amount of the metal salt of an organic dithiophosphorlc acid is between 02 and 2.0% by weight of the mineral oil base and the amount of the metal salt of petroleum sulphonic acid is between 0.05 and 2.0% by weight of the mineral oil base.

11. A lubricating composition in accordance with claim 1 in which the metal salt is a chro- 14 mium salt of said organic dithiophosphoric acid.

12. A lubricating composition in accordance with claim 1 in which the metal salt is a zinc salt of said organic dithiophosphoric acid.

13. A lubricating composition in accordance with claim 1 in which the metal salt is a cobalt salt of said organic dithiophosphoric acid.

14. A lubricating composition in accordance with claim 1 in which the metal salt is a magnesium salt of said organic dithiophosphoric acid.

15. A lubricating composition in accordance with claim 1 in which the metal salt is a manganese salt of said organic dithiophosphoric acid.

ELLIOTT ALFRED EVANS. JOHN SCOTCHFORD ELLIOTT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,125,936 Liberthson Aug. 9, 1938 2,241,243 Conary et al May 6, 1941 2,252,984 Rutherford et a1. Aug. 19, 1941 2,344,395 Cook et a1 Mar. 14, 1944 2,369,632 Cook Feb. 13, 1945 2,372,244 Adams et a1 Mar. 27, 1945 2,382,775 Cook et a1. Aug. 14, 1945 2,417,876 Lewis et a1 Mar. 25, 1947 2,418,422 Palmer Apr. 1, 1947 

1. A LUBRICATING COMPOSITION COMPRISING AS A MAJOR INGREDIENT A MINERAL OIL BASE, SAID BASE 